Quantitative comparison of 2D and 3D circumferential strain using MRI tagging in normal and LBBB hearts

Mapping right ventricular myocardial mechanics using 3D cine DENSE cardiovascular magnetic resonance

BACKGROUND

The mechanics of the right ventricle (RV) are not well understood as studies of the RV have been limited. This is, in part, due to the RV's thin wall, asymmetric geometry and irregular motion. However, the RV plays an important role in cardiovascular function. This study aims to describe the complex mechanics of the healthy RV using three dimensional (3D) cine displacement encoding with stimulated echoes (DENSE) cardiovascular magnetic resonance (CMR).

METHODS

Whole heart 3D cine DENSE data were acquired from five healthy volunteers. Tailored post-processing algorithms for RV mid-wall tissue tracking and strain estimation are presented. A method for sub-dividing the RV into four regions according to anatomical land marks is proposed, and the temporal evolution of strain was assessed in these regions.

RESULTS

The 3D cine DENSE tissue tracking methods successfully capture the motion and deformation of the RV at a high spatial resolution in all volunteers. The regional Lagrangian peak surface strain and time to peak values correspond with previous studies using myocardial tagging, DENSE and strain encoded CMR. The inflow region consistently displays lower peak strains than the apical and outflow regions, and the time to peak strains suggest RV mechanical activation in the following order: inflow, outflow, mid, then apex.

CONCLUSIONS

Model-free techniques have been developed to study the myocardial mechanics of the RV at a high spatial resolution using 3D cine DENSE CMR. The consistency of the regional RV strain patterns across healthy subjects is encouraging and the techniques may have clinical utility in assessing disrupted RV mechanics in the diseased heart.

Rapid and accurate left ventricular chamber quantification using a novel CMR segmentation algorithm: a clinical validation study

PURPOSE

To evaluate the clinical performance of a novel automated left ventricle (LV) segmentation algorithm (LV-METRIC) that involves no geometric assumptions.

MATERIALS AND METHODS

LV-METRIC and manual tracing (MT) were used independently to quantify LV volumes and LVEF (ejection fraction) for 151 consecutive patients who underwent cine-CMR (steady-state free precession). Phase contrast imaging was used to independently measure stroke volume.

RESULTS

LV-METRIC was successful in all cases. Mean LVEF was within 1 point of MT (Delta 0.6 +/- 2.3%, P < 0.05), with smaller differences among patients with (0.5 +/- 2.5%) versus those without (0.9 +/- 2.3%; P = 0.01) advanced systolic dysfunction (LVEF <or= 35% by MT). LV volumes by LV-METRIC were slightly smaller than MT during end-diastole (3.9 +/- 6.8 mL, P < 0.001) and end-systole (1.4 +/- 5.5 mL, P < 0.01). Mean processing time was 22 +/- 13 seconds for LV-METRIC and 4:59 +/- 1:56 minutes for MT (P < 0.001). Processing time correlated with LV blood volume by MT (r = 0.43) and LV-METRIC (r = 0.55), but slope was 10-fold steeper for MT (0.02 vs. 0.001), indicating greater proportionate time increases in relation to chamber dilation. Compared to stroke volume by phase contrast, LV-METRIC yielded smaller differences (0.3 +/- 18.3 mL) than MT (2.5 +/- 17.2 mL; P < 0.001).

CONCLUSION

Among a broad series of consecutive patients undergoing CMR, automated LVEF by LV-METRIC was within 1 point of MT with processing time reduced 14-fold. Stroke volume by LV-METRIC yielded improved agreement with an independent standard of phase contrast imaging.

Quantitative analysis of intraventricular dyssynchrony using wall thickness by multidetector computed tomography

OBJECTIVES

We sought to determine the feasibility of cardiac computed tomography (CT) to detect significant differences in the extent of left ventricular dyssynchrony in heart failure (HF) patients with wide QRS, HF patients with narrow QRS, and age-matched controls.

BACKGROUND

The degree of mechanical dyssynchrony has been suggested as a predictor of response to cardiac resynchronization therapy. There have been no published reports of dyssynchrony assessment with the use of CT.

METHODS

Thirty-eight subjects underwent electrocardiogram-gated contrast-enhanced 64-slice multidetector CT. The left ventricular endocardial and epicardial boundaries were delineated from short-axis images reconstructed at 10% phase increments of the cardiac cycle. Global and segmental CT dyssynchrony metrics that used changes in wall thickness, wall motion, and volume over time were assessed for reproducibility. We defined a global metric using changes in wall thickness as the dyssynchrony index (DI).

RESULTS

The DI was the most reproducible metric (interobserver and intraobserver intraclass correlation coefficients >/=0.94, p < 0.0001) and was used to determine differences between the 3 groups: HF-wide QRS group (ejection fraction [EF] 22 +/- 8%, QRS 163 +/- 28 ms), HF-narrow QRS (EF 26 +/- 7%, QRS 96 +/- 11 ms), and age-matched control subjects (EF 64 +/- 5%, QRS 87 +/- 9 ms). Mean DI was significantly different between the 3 groups (HF-wide QRS: 152 +/- 44 ms, HF-narrow QRS: 121 +/- 58 ms, and control subjects: 65 +/- 12 ms; p < 0.0001) and greater in the HF-wide QRS (p < 0.0001) and HF-narrow QRS (p = 0.005) groups compared with control subjects. We found that DI had a good correlation with 2-dimensional (r = 0.65, p = 0.012) and 3-dimensional (r = 0.68, p = 0.008) echocardiographic dyssynchrony.

CONCLUSIONS

Quantitative assessment of global CT-derived DI, based on changes in wall thickness over time, is highly reproducible and renders significant differences between subjects most likely to have dyssynchrony and age-matched control subjects.

Comparison of 2D and 3D calculation of left ventricular torsion as circumferential-longitudinal shear angle using cardiovascular magnetic resonance tagging

PURPOSE

To compare left ventricular (LV) torsion represented as the circumferential-longitudinal (CL) shear angle between 2D and 3D quantification, using cardiovascular magnetic resonance (CMR).

METHODS

CMR tagging was performed in six healthy volunteers. From this, LV torsion was calculated using a 2D and a 3D method. The cross-correlation between both methods was evaluated and comparisons were made using Bland-Altman analysis.

RESULTS

The cross-correlation between the curves was r2 = 0.97 +/- 0.02. No significant time-delay was observed between the curves. Bland-Altman analysis revealed a significant positive linear relationship between the difference and the average value of both analysis methods, with the 2D results showing larger values than the 3D. The difference between both methods can be explained by the definition of the 2D method.

CONCLUSION

LV torsion represented as CL shear quantified by the 2D and 3D analysis methods are strongly related. Therefore, it is suggested to use the faster 2D method for torsion calculation.

Characterization of three-dimensional myocardial deformation in the mouse heart: an MR tagging study

PURPOSE

To develop a 3D MR tagging method that combines harmonic phase (HARP) and homogeneous strain analysis methods for quantification of regional myocardial wall motion in mice.

MATERIALS AND METHODS

3D tagged images were acquired from seven C57BL/6 mice. Intersecting tag points were reconstructed and 3D strains were quantified at apical, midventricular, and basal levels. Circumferential and radial strains quantified with 2D MR tagging were compared with those calculated from 3D tagged images.

RESULTS

Our data showed significant heterogeneity in radial, circumferential, and shear strains. Longitudinal strain was more homogeneous. The circumferential-longitudinal shear strain, a unitless measure of ventricular torsion, was positive throughout the left ventricle. There were strong correlations between 2D and 3D studies at the basal and midventricular levels.

CONCLUSION

This work demonstrates the feasibility of 3D characterization of cardiac function in mouse via the combination of HARP and homogeneous strain analysis.

Potential uses of computed tomography for management of heart failure patients with dyssynchrony

Cardiac resynchronization therapy has become an integral part in the step-care approach to manage patients with heart failure. Cardiac imaging remains central to appropriate patient selection and optimal left ventricular lead placement, both of which are important determinants of response to cardiac resynchronization therapy. One of the biggest limitations with current imaging modalities is the inability of a single technique to address each, the anatomic (venous anatomy), mechanical (dyssynchrony), and structural (extent of scar location) issues accompanying cardiomyopathy. We present here the potential concept of using cardiac computed tomography as a single modality to acquire functional and anatomic information, and also to show the possibility of integrating this with real time fluoroscopy.